New York says Secretary of State Rex Tillerson used an email alias to discuss climate change while he was Exxon Mobil’s chief executive.

Mr Tillerson sent messages from the account to discuss the risks posed by climate change, New York Attorney General Eric Schneiderman said in a court filing about his office’s fraud investigation of the company. Mr Tillerson, whose middle name is Wayne, used the Wayne Tracker account on the Exxon system from at least 2008 to 2015, Schneiderman said.

Schneiderman made the claim in a letter Monday to Justice Barry Ostrager in New York state court in Manhattan, accusing Exxon of failing to turn over all relevant documents required by a court order.

The filing comes in a protracted legal dispute in which Exxon seeks to derail probes by New York and Massachusetts into whether the company misled investors for years about the possible impact of climate change on its business.

Mr Tillerson used the account for “secure and expedited communications between select senior company officials and the former chairman for a broad range of business-related topics,” after his primary account began receiving too many messages, Exxon spokesman Alan Jeffers said in an email.

New York’s claim marks the latest email-handling matter to make headlines in Washington, from Hillary Clinton using a private email server as Secretary of State to more-recent revelations that Vice President Mike Pence used a private email account to conduct some official business as governor of Indiana. Neither of those instances involved an alias.